The basic design features of power tongs and back-up units having guided jaws is illustrated in U.S. Pat. No. Re. 31,699, re-issued Oct. 9, 1984 and invented by Emory L. Eckel. The basic configuration for this type of unit included an open end through which a pipe was inserted into the back-up unit. The frame contained a member having a camming surface thereon. Concentrically nested within this member was a spider. Slidably mounted within slots within the spider were jaws whose rollers tracked the camming surface. When relative motion between the member having the camming surface and the spider occurred, radial displacement of the jaw within said slots would occur until the jaws were radilly displaced and a die contacted the pipe.
Since power tongs and back-up units operate in a fairly dirty environment, the clearance within the spider must be sufficient to prevent jamming of the jaw members due to foreign matter which may become lodged in the clearance. The purpose of the spider and clearance combination was also to provide a guide for the jaw. However, due to the clearance employed to prevent jamming of the jaw, the spider, in practice, did not guide the jaw at all. In fact, to achieve any guiding effect by the spider, the jaw is required to pivot within the clearance. The only way the jaw could pivot was first to gouge or deform the pipe.
Upon contact between the die rigidly mounted in the jaw and the pipe, further rotational movement of the jaw was possible due to the clearance. This further movement after initial contact of the die with the pipe, in effect, resulted in a very high load at the leading end of the die. This phenomenon caused damage to the outer pipe wall, and in some cases, physically deformed the pipe due to the excessive line loads applied.
It is the object of this invention to improve the jaw design in a guided jaw power tong or back-up unit such that there is close to an equally distributed load applied to the pipe. It is another object of this invention to movably mount the die to the jaw in an effort to equalize the loads applied by the die mounted to the jaw on the pipe. It is yet another object of this invention to actually use the spider as a guide for the jaw, while at the same time, using movably mounted dies mounted to the jaw. The guiding of the spider coupled with the movable mounting of the die prevents the possibility of the die deforming the pipe and/or gouging the pipe surface.